Nivkh (/ˈniːfk/ NEEFK; occasionally also Nivkhic; self-designation: Нивхгу диф, Nivhgu dif, /ɲivxɡu dif/), Gilyak (/ˈɡɪljæk/ GIL-yak), or Amuric, is a small language family, often portrayed as a language isolate, of two or three mutually unintelligible languages spoken by the Nivkh people in Outer Manchuria, in the basin of the Amgun (a tributary of the Amur), along the lower reaches of the Amur itself, and on the northern half of Sakhalin. "Gilyak" is the Russian rendering of terms derived from the Tungusic "Gileke" and Manchu-Chinese "Gilemi" (Gilimi, Gilyami) for culturally similar peoples of the Amur River region, and was applied principally to the Nivkh in Western literature.

The population of ethnic Nivkhs has been reasonably stable over the past century, with 4,549 Nivkhs counted in 1897 and 4,673 in 1989. However, the number of native speakers of the Nivkh language among these dropped from 100% to 23.3% in the same period, so by the 1989 census there were only 1,079 first-language speakers left. That may have been an overcount, however, as the 2010 census recorded only 198 native speakers, less than 4% of the ethnic population.

Proto-Nivkh(ic), the proto-language ancestral to the modern-day languages, has been reconstructed by Fortescue (2016).

Nivkh is a dialect continuum. There is a high degree of variability of usage among Nivkhs depending on village, clan, and even the individual speaker. Varieties are traditionally grouped into four geographic clusters. These are the lower-Amur variety, the North Sakhalin variety (spoken on the coasts around the Amur Liman, including the mainland and west Sakhalin), the East Sakhalin variety (including populations around the Tym River), and the South Sakhalin variety (spoken around the Poronay River). The lexical and phonological differences across these varieties is great enough that specialists describe them as falling into two or three languages, though for purposes of language revival among a small and already divided population, Nivkh is generally presented as a single language, due to fears of the consequences of further division.

Gruzdeva (1998) notes that speakers of East Sakhalin and the lower Amur cannot understand each other, and divides the varieties into two languages, Nivkh proper (including the lower Amur, Northern Sakhalin / Straits and Western Sakhalin varieties) and Nighvng (the East and South Sakhalin varieties). Fortescue (2016) notes that the Amur, East Sakhalin and South Sakhalin varieties have low intelligibility with each other, and considers each of them to constitute a separate language.

Nivkh is not known to be related to any other language, making it a language isolate. For convenience, it may be included in the geographical group of Paleosiberian languages. Many words in the Nivkh languages bear a certain resemblance to words of similar meaning in other Paleosiberian languages, Ainu, Korean, or Tungusic languages, but no regular sound correspondences have been discovered to systematically account for the vocabularies of these various families, so any lexical similarities are considered to be due to chance or to borrowing.

Michael Fortescue suggested in 1998 that Nivkh might be related to the Mosan languages of North America. Later, in 2011, he argued that Nivkh, which he referred to as an "isolated Amuric language", was related to the Chukotko-Kamchatkan languages, forming a Chukotko-Kamchatkan–Amuric language family. However, Glottolog considers the evidence to be "insufficient".

In 2015, Sergei Nikolaev argued in two papers for a systematic relationship between Nivkh and the Algic languages of North America, and a more distant relationship between these two together and the Wakashan languages of coastal British Columbia.